DC voltage from Network cable.

[alphacat]

Hey.

Is any DC voltage supplied from the network cable?

I thought of connecting a network cable to a product i got and have the network cable powering the the product (The product needs only 2V to be powered up).

Is it possible?

Thank you.

 

[smanches]

Search for Power over Ethernet. Not much power there, but about 12-15W though.

 

[alphacat]

My idea was to connect such wire (see picture) from the modem to the product.
How do i know what DC voltage does this cable carry, and which wire carries the DC voltage?

 

[smanches]

I believe you need a splitter, or build the splitter into your product. The power comes over the same lines as the data, I believe as a DC offset of some sort. Haven't really looked into the details.

There is a ton of information and LOTS of products for it now.

 

[Sceadwian]

The power only comes if the device specifically states that it supports Power over Ethernet, standard Ethernet cables do not ordinarily contain DC voltages.

Power over Ethernet - Wikipedia, the free encyclopedia

All 802.1X devices are required to be transformer isolated so DC voltages can not be passed, POE is 802.3af

For standard ethernet cables Pins 1 and 2 are RX and 3 and 6 are TX, Pairs 4+5 and 7+8 carry +VCC and -VCC respectivly, with max ratings of 30-50 volts or so. Use of a DC-DC converter is obviously required for many applications.

You could design a custom adapter that would bring pins 4/5 and 7/8 to outside connections and use them yourself, as stated 10BT adapters are required to be transformer isolated so it's safe even if the card/connector are wired wrong. For the voltages you're askign for it's not complicated, however currents must be kept low or it will interfere with the data side of things.

 

[smanches]

On 1000BT, all four pairs are used. Basically they use the phantom power technique like they use to power microphones from the actual signal lines.

Power and data are on the same pairs.

 

[Sceadwian]

That's all covered in the Wikipedia article smanches. The implementation would also be identical except the wires not ordinarily used on 10/100BT ethernet would have to be wired straight through. I would however be incredibly paranoid about power filtering if you intend to get the fully specificied bandwidth of gigabit ethernet with power going over it. Common mode noise reduction is limited in the real world =)

 

[alphacat]

Thank you very much guys.
I read about the POE technology.

I didnt quite understand how the Network Switches work yet, but i'll get to that also.

My product is powered up by 2V-3.6V.
Is it possible to get a voltage at this range from the Category 5 cable?
I read that the min voltage available is 44V, is it possible to somehow get (much) less than that?

Thanks.

 

[smanches]

Use a micro buck converter to drop the voltage down to what you need. They make self-contained modules that do not require any external parts.

 

[alphacat]

Thank you.

Who are "they"?
The POE manufacturers?

 

[smanches]

They, meaning electronic component manufacturers. Should be able to find them online at any decent electronics place. I know Digikey and Mouser both have them.

 

[alphacat]

Got you, thanks a lot fellow.

 

[smanches]

These are the ones I was talking about. Although it looks like the highest input voltage is only 28Vdc.

DC DC Converters | Digi-Key